Mr. W. Clark on the Animal of Kellia rubra. 455 



instead of being an open-mantled animal, is one of the closed 

 moUusca,-— where, in this case, is the entrance for the branchial 

 currents ? The only answer that can be given is, at the poste- 

 rior branchial slit, and the discharge of the water must be at the 

 sa7ne aperture. In this bivalve the faeces are, as I have repeatedly 

 seen, discharged from the rectum in minute pellets into the 

 branchial slit, which in this animal undoubtedly performs three 

 functions, those of ingress and egress of branchial currents, and 

 a conduit for the faeces. 



It may be asked, why has nature departed from her usual 

 branchial scheme only in Kellia rubra and K. suborhicularis ? We 

 will now examine into the " cui bono" of this fold of the mantle, 

 considered as a branchial appendage. It is well known that 

 nature never acts by way of surplusage ; and having given Kellia 

 rubra an open mantle by which the currents can enter, as in 

 other analogous open bivalves, we must conclude she has not 

 departed from her usual scheme, and that this fold is not a spe- 

 cial branchial organ, but is intended to fulfill other functions. 



I will mention what perhaps may be considered a conclusive 

 proof that the tube-like fold of the mantle cannot be intended 

 for the ingress of branchial currents, which is, that the animal 

 very often thrusts its foot into the fold, and by the with- 

 drawal of which it is opened and the edges separated. How 

 then can a fold, whose form by this action is continually changing, 

 and is subject to momentary interruption, be the conduit of 

 regular, delicate, and uninterrupted branchial currents ? 



May we not infer from this constant alliance of the foot with 

 the fold, that there is a more intimate functional connexion be- 

 tween them, perhaps of a locomotive nature ? 



I will now very shortly state the grounds of my conjecture, 

 that the fold in question is to aid the animal in locomotion. 



The habitat of this singular creature is at a far greater eleva- 

 tion in the littoral zone than any other bivalve, and nearly as far 

 removed from the level of the water as the Littorina petrcea, which 

 is at no time completely submerged in the sea. The Kellia rubra 

 on the Devon coast near Exmouth is generally imbedded in the 

 Lichina pxjgmcea, which grows in the cavities of rocks of such, 

 considerable elevation and so near the land, that thousands of 

 these animals pass their entire existence without perhaps ever 

 being completely in a condition to receive branchial currents of 

 sea-water ; even the spray rarely reaches them except in gales of 

 wind. It appears then that the tides washing the bases of their 

 rocky habitat, combined with the saline mixture of atmospheric 

 particles, supply a sufficient humidity for the growth of the Li- 

 china pygnKsa and the sustentation and welfare of the bivalve 



